The present invention relates to apparatus by which the photographic density of a developed film is photoelectrically measured.
Generally in a photographic film processor, in order to recover the activity of a developer or developing solution once declined after the process of development, a new developer or replenisher is to be replenished. Particularly in the film processor for lithographic film or the like which requires high accuracy, since the result of the development is considerably influenced by the under or over replenishment of the developer, the replenishment is controlled in accordance with the measured value obtained through measuring the photographic density of the developed film.
Concerning the measuring method of photographic density of a film, as exemplified in Japan Patent Application laid open under No. 56-154650, a method is known wherein a linear light source is arranged on one side across a carrier route of the film and a linear light receiver is oppositely arranged on the counter side respectively, thereby measuring a quantitative difference between an incident light to the light receiver when there is no film between the light source and the light receiver and the incident light when the film is carried through between the light source and the light receiver. In this method, however, measurement error is serious since only the average photographic density in rather wide area can be measured.
On the other hand, as exemplified in Japan Patent Application laid open under No. 50-27544, another attempt is proposed wherein a plurality of light receiving elements are arranged at equal spacing therebetween in place of the linear light receiver so as to scan the film carried and to make integral addition of the output signals from each of the light receiving elements altogether, thereby measuring photographic density. In this method, it is necessary to straighten the light receiving characters of the plurality of the light receiving elements arranged across the carrier route, and accordingly it is also necessary to adjust the sensitivity of the plurality of light receiving elements one by one when assembling thereof. However, it is quite difficult to get a linear light source emitting an uniform quantity of light over the full length thereof, and besides it takes long for the adjustment. Consequently, it may be said that the wider the measuring width of the film or the more the number of light receiving element, the more difficult the said adjustment.
Further, in the conventional measurement device of photographic density of a film, it is generally adjusted not to replenish the developer when the photographic density is under 5% approx. This is because, even in case of a transparent film, the transmission of light is usually impeded by 5% or so, and because, without such adjustment, the replenishment will be unnecessarily effected even to the transparent film not bearing the photographic density at all yet. In the said conventional measurement device with adjustment as above-described, however, when a film having a narrower width than the effective measuring width and having rather smaller photographic density area is applied to the measurement device, or as an extreme case when a film having its width less than 5% of the effective measuring width and already bearing a full photographic density is applied thereto, so far as the measured value is under 5%, the replenishment is not carried out in spite of already bearing the photographic density, resulting in the aggravation of the development process thereafter.
It is, therefore, an object of the present invention to provide a measurement device for exactly measuring photographic density of a film without foregoing adjustment as well as irrespective of the width of the applied film by obtaining a rate of change in the form of a ratio between the reference signal decided immediately before carrying the film and the actual output signal of the light receiving element when the film is carried.
Thus, in accordance with the present invention, there is provided, in a measurement device of photographic density of a film wherein a light source is provided on one side over a film carrier route and a plurality of light receiving elements for converting the transmitted light of a film emitted from the said light source to an electrical signal are provided on the counter side of the said light source forming a line, a device for measuring photographic density of the film comprising a means for obtaining a rate of change in the form of a ratio between a reference signal decided beforehand for each of the light receiving elements and an output signal of the light receiving elements when the film is carried, and a means for obtaining photographic density of the film in accordance with the said ratio.
More particularly, by the foregoing formation, the present invention contemplates a measurement device of photographic density of a film having its advantages and features as follows:
(i) By adding the rate of change between the reference signal and the output signal of the light receiving elements after being obtained the said rate in the form of a ratio, it is neither necessary to straighten the light receiving characters of each of the light receiving elements being different from the conventional method, nor necessary to have a light source whose quantity of light must be uniform over the full length.
(ii) Even in case of the photographic density in the width under 5% of the effective measuring width of an automatic developing machine, the replenishment is exactly carried out through measuring each of the light receiving elements.
(iii) When the reference signal is obtained, by taking an arithmetic mean of several output signals, the change in the quantity of light can be appropriately adjusted, and further by making compensation at the interval of every 5 seconds, for example, the said change can be more effectively controlled.
(iv) As the output signal is monitored for each of the light receiving elements, even in case of a failure in some of the light receiving elements, the control can be made without difficulty.
Other objects, features and advantages of the present invention will become apparent in the cource of the following description with the accompanying drawings.